Tuned filters have been employed for a number of years to decode scrambled or protected television signals. U.S. Pat. No. 4,451,803 discloses a notch filter, for example, that includes two separate electrically interconnected filter sections mounted on a common circuit board. The two filter sections are magnetically isolated through an isolation area defined by an isolation shield. The common circuit board is placed within a filter housing having one open end and an integral connector located at the other end. An end cap is then attached to the open end of the filter housing with a press fit. The filter housing with attached end cap is then located within an outer sleeve by sliding the filter housing into an open end of the outer sleeve. A press-fit is commonly used as the securing mechanism to retain the filter housing within the outer sleeve housing.
A potential problem has been identified with regard to the conventional filter structures that utilize a press-fit to retain the filter housing within the outer sleeve, namely, the press-fit has occasionally failed, thereby allowing the filter housing to freely rotate within the outer sleeve. The failure of the press-fit may result from tolerance build-up, natural variations in the hardness of the outer sleeve or processing variations in the manufacturing process. Regardless of the cause, the spinning or rotation of the filter housing with respect to the outer sleeve has caused concerns among users of the filters over possible poor sealing of the filter structure against moisture and possible problems related to RFI emissions or leakage. In view of the above, it would be desirable to provide a filter structure of inexpensive design that would reliably prevent rotation of the filter housing with respect to the outer sleeve in the event of failure of the securing mechanism.